Physical cosmology, as it is now understood, began with the twentieth century development of Albert Einstein's general relativity|general theory of relativity and better astronomical observations of extremely distant objects. These advances made it possible to speculate about the origin of the universe, and allowed scientists to establish the Big Bang as the leading cosmological model. Few researchers still advocate any of a handful of alternative cosmologies, and professional cosmologists generally agree that the Big Bang best explains observations.
Cosmology draws heavily on the work of many disparate areas of research in physics. Areas relevant to cosmology include particle physics experiments and theory, including string theory, astrophysics, general relativity, and plasma physics. Thus, cosmology unites the physics of the largest structures in the universe with the physics of the smallest structures in the universe.